Specific substances under search or to be screened, such as drugs or habit-forming substances hormones, viral, bacterial and parasitic antigens, as well as substances shich could be indicative of specific illnesses (e.g. tumor markers) or the like. can be detected in body fluids such as urine or blood by agglutination reactions. The agglutination occurs in a mixture of an antibody reagent, a reagent comprising a latex coated with a substance under search or metabolite thereof, and the body fluid. The quantity of antibodies in the antibody reagent is limited and they can combine both with the substance under search or metabolite in the latex and with the substance under search in the body fluid. Agglutinations form only if, owing to the absence of the substance under search or metabolite in the body fluid there is a sufficient quantity of antibodies to react with the latex particles. Then, a number of latex particles can agglomerate into visually definable agglutinations. If the substance under search or metabolite is present in the body fluid, there are far fewer antibodies available for agglutination, since the antibodies form an immune complex with the substance under search or metabolite in the body fluid. In that event, the agglutination reaction is very weak or non-existent.
Another type of assay for determining substances of the above-mentioned kind can be carried out by means of agglutination reactions which under certain conditions can take place in a mixture of a reagent comprising a latex coated with an antibody directed against the substance to be determined. In such a mixture visually definable agglutinations form only if there is a sufficient quantity of the substance being sought in the body fluid, whereas no agglutination takes place if the substance being sought is absent in the body fluid under examination. Antibodies in blood or other body fluids can also be determined in a similar way, in which case the corresponding substances or antigens or even also antibodies, which are directed against the substance being sought can be used as agglutination partner in the agglutination system.
In one method of immunological testing of the aforementioned kind, a sample and reagents are poured into a test-tube mixed and kept reacting for some time by shaking and tilting the test-tube by hand. This procedure can result in different agglutination reactions depending on the duration and intensity of shaking and tilting the test-tube. In view of the resulting uncertainty in evaluating the reaction results, it has been suggested (DE-A-35 37 734 and US-A-4,596,695) to conduct the agglutination reaction in a reaction capillary. As a result, there is no need for manually spinning or shaking the sample-reagents mixture, since the movement of the mixture produced by capillary action along the reaction capillary ensures that the sample is mixed with the reagents and that a continuous motion of the sample-reagent mixture takes place for a given time suitable for forming agglutinations.
In this known test device the reaction capillary is disposed between two transparent glass plates which form a capillary chamber by being held at a set constant distance from one another. The capillary action on the respective sample-reagents mixture is therefore substantially constant along the chamber.
Under these conditions, the reaction sensitivity and also the reproducibility of the reaction results are disadvantageously subject to wide fluctuations. This is because, when a given test is performed in different ways, the sample-reagents mixture takes different times to flow through the capillary chamber. Thus, an important criterion for obtaining reproducible results is the maintenance of uniform reaction times. Another condition for optimum sensitivity of the agglutination reaction is that the reaction be given a fixed time to occur (e.g., 3 minutes) with only slight deviations upward or downward.